Multiple riser fluidized catalytic cracking process employing a mixed catalyst

Abstract

A catalytic cracking process is described featuring multiple risers in which a variety of hydrocarbon conversion reactions takes place, a stripping unit in which entrained hydrocarbon material is removed from catalyst and a regeneration zone in which spent cracking catalyst is regenerated, which comprises: (a) converting a relatively high boiling hydrocarbon charge material in a first riser in the presence of a catalyst mixture comprising, as a first catalyst component, an amorphous cracking catalyst and/or a large pore crystalline cracking catalyst and, as a second catalyst component, a shape selective medium pore crystalline silicate to provide lighter products including naphtha and C3 and/or C4 olefin; (b) converting an ethylene-rich charge material introduced to a second riser at a lower level thereof in the presence of said catalyst mixture to provide heavier products and to increase the temperature of the catalyst in said region; and, (c) converting C3 and/or C4 olefin introduced to the second riser at a higher level thereof in the presence of said catalyst mixture to provide a relatively high octane gasoline product.

What is claimed is: 
     
       1. A fluidized catalytic cracking (FCC) process for cracking in a first riser reactor a heavy feed to cracked products comprising lighter products including light olefins comprising ethylene, and olefinic gasoline over a catalyst mixture comprising a FCC catalyst and a shape selective zeolite additive said process characterized by: (a) recovering as a product the gasoline fraction produced by riser cracking of the heavy feed in the first riser;   (b) recovering an ethylene rich charge material consisting essentially of catalytically cracked products and comprising at least 10 weight percent ethylene and the balance comprising propylene and butylene and mixtures thereof;   (c) separately recovering a light olefinic feed with a higher boiling point than the ethylene rich material, comprising C 3  and C 4  olefins and mixtures thereof;   (d) contacting in the base of a second riser reactor a feed consisting essentially of the ethylene rich charge material with the FCC catalyst and shape selective zeolite additive at a temperature of 400°-750° F.;   (e) converting in an exothermic conversion reaction a majority of the ethylene rich charge material in the base of the second riser to C 5   +  as an intermediate product;   (f) contacting the mixture of C 5   +intermediate  product and catalyst with the light olefinic feed comprising C 3  and C 4  olefins and mixtures thereof;   (g) reacting the C 5   30  intermediate product with the light olefinic feed to form high octane gasoline which is discharged from the second riser.   
     
     
       2. The process of claim 1 wherein the ethylene-rich charge material is essentially pure ethylene. 
     
     
       3. The process of claim 1 wherein the FCC catalyst comprises a large pore zeolite selected from the group consisting of zeolite X, Y, REY, USY, RE-USY, mordenite and mixtures thereof. 
     
     
       4. The process of claim 1 wherein the shape selective zeolite additive is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48. 
     
     
       5. The process of claim 3 wherein, the first riser, the shape selective zeolite additive is about 0.1 to about 10 weight percent of the total catalyst mixture, the first riser operates at reaction conditions including a temperature of about 900 to about 1150 F., a catalyst to oil ratio of about 3:1 to about 20:1 and a catalyst contact time of about 0.5 to about 30 seconds. 
     
     
       6. The process of claim 5 wherein the shape selective zeolite additive is about 0.2 to about 5.0 weight percent of the catalyst mixture, the temperature is about 925 ° to about 1000° F., the catalyst to oil ratio is about 4:1 to about 10:1 and the catalyst contact time is about 1 to about 15 seconds. 
     
     
       7. The process of claim 3 wherein, in the first riser, the shape selective zeolite additive is about 1 to about 25 weight percent of the total catalyst mixture, the first riser operates at reaction conditions including a temperature of about 900 to about 1150 F., a catalyst to oil ratio of about 3:1 to about 20:1 and a catalyst contact time of about 0.5 to about 30 seconds. 
     
     
       8. The process of claim 7 wherein the shape selective zeolite additive is about 2 to about 10 weight percent of the total catalyst mixture. 
     
     
       9. The process of claim 1 wherein the second riser has a lower region above the base and in the lower region of the second riser, the shape selective zeolite additive is about 1 to about 25 weight percent of the catalyst mixture and reaction conditions in said lower region include a temperature of about 400 to about 750 F., a catalyst to hydrocarbon ratio of about 5:1 to about 40:1 and a catalyst contact time of about 10 to about 90 seconds. 
     
     
       10. The process of claim 9 wherein the shape selective zeolite additive is about 2 to about 10 weight percent of the total catalyst mixture, the temperature is from 500° to about 650° F., the catalyst to hydrocarbon ratio is about 20:1 to about 30:1 and the catalyst contact time is about 50 to about 70 seconds. 
     
     
       11. The process of claim 1 wherein the second riser has an upper region above the lower region and the reaction conditions in the upper region of the second riser include a temperature of about 400 to about 750 F., the catalyst to light olefinic feed ration of from about 5:1 to about 40:1 and a catalyst contact time of about 5 to about 45 seconds. 
     
     
       12. The process of claim 11 wherein the temperature in the upper region of the second riser reactor is about 500° to about 650° F., the catalyst to light olefinic feed ratio is about 20:1 to about 30:1 and the catalyst contact time is about 25 to about 35 seconds. 
     
     
       13. The process of claim 1 wherein the average particle size of the FCC catalyst is greater than that of the shape selective zeolite additive. 
     
     
       14. The process of claim 1 wherein the average particle size of the shape selective zeolite additive catalyst is greater than that of the FCC catalyst. 
     
     
       15. The process of claim 14 wherein the average particle size of the FCC catalyst is about 20 to about 150 microns and the average particle size of the shape selective zeolite additive is about 500 to about 70,000 microns, and the average packed density of the FCC catalyst ranges from about 0.4 to about 1.1 gm/cm 3  and the average packed density of the shape selective zeolite additive ranges from about 0.6 to about 4.0 gm/cm 3 . 
     
     
       16. The process of claim 15 wherein the average particle size of the FCC catalyst is about 50 to about 100 microns and the average particle size of the shape selective zeolite additive is about 1000 to about 25,000 microns, and the average packed density of the FCC catalyst is about 0.6 to about 1.0 gm/cm 3  and the average packed density of the additive is about 2.0 to about 3.0 gm/cm 3 . 
     
     
       17. The process of claim 16 wherein the additive is composited with a matrix material which imparts a density greater than the density of the FCC catalyst. 
     
     
       18. The process of claim 17 wherein additive is composited with a matrix material which possesses a coking rate which is higher than the coking rate of the FCC catalyst. 
     
     
       19. The process of claim 1 wherein the density of the shape selective zeolite additive is greater than the density of the FCC catalyst. 
     
     
       20. The process of claim 1 wherein the shape of the shape selective zeolite additive is different from the shape of the FCC catalyst. 
     
     
       21. The process of claim 20 wherein the average particle size of the shape selective zeolite additive is larger than the average particle size of the FCC catalyst. 
     
     
       22. The process of claim 21 wherein the density of the shape selective zeolite additive is greater than the density of the FCC catalyst.